1. Field of the Invention
The present invention relates to a multipole switch for medium voltage and high voltage.
2. Description of the Related Art
In order to keep the transients produced as a result of switching operations in medium-voltage and high-voltage networks as small as possible, switches are connected and/or disconnected such that they are synchronized in time with the network voltage or with the network current. An optimum reduction in the transients is achieved if, in the case of multipole switching, either all the poles are switched individually at different times or at least one pole is switched such that it is staggered in time with respect to the other poles, depending on the load to be switched. In a three-phase network, for example when connecting a capacitor bank, the transient currents are reduced most when the touching of the contacts in the individual poles in each case takes place at the time of the voltage zero crossing of the applied voltage. In this case, if both the star point of the supplying network and the star point of the capacitor bank are grounded, the three poles of the switch are closed, in a preferred manner, at intervals of in each case one sixth of a cycle, that is to say at an interval of 3 and 1/3 ms in a 50 Hz network. If, on the other hand, one of the star points is not grounded or is grounded only via a large impedance, two poles are preferably closed simultaneously first, and the third pole is closed with a delay of a quarter of a cycle, that is to say after 5 ms in a 50 Hz network. Optimum conditions for the suppression of transients during the connection of transformers and inductor coils can be achieved in an analogous manner if they are connected at the instant of the maximum value of the relevant phase voltage. Overvoltages can also be reduced in a corresponding manner during disconnection, by staggered switching of poles.
If each pole of a switch is driven by its own drive, the time stagger of the individual poles can be implemented in a simple manner by means of an electronic controller, for example a timing relay. However, if the individual poles of a switch are driven by a drive which is common to all the poles, the staggering of the poles must be implemented by the design of the mechanical transmission system for transmitting the switching movement from the drive to the moving switch contact pieces of the individual poles.
A switch of this type is disclosed in DE-A-3810453. Each pole has an interrupter unit whose moving switch contact piece is articulated, via an insulating rod, on a lug-like connecting element which is connected at the other end to a double-armed angled lever which can pivot about an axis. The double-armed angled levers are articulated on an operating rod which is common to all the poles and can be moved in a reciprocating manner by means of a drive. The staggering of the individual interrupter units is achieved in the case of this known switch by the angle of the toggle-lever joint between the respective connecting element and that arm of the double-armed angled lever which is connected to it in an articulated manner extending differently for the various poles. In this case, this different extent can be achieved by varied measures, such as different lengths of the connection elements and differently angled double-armed angled levers.
If this known transmission system is used in a switch in which one drive shaft per interrupter unit passes through a housing in a sealed manner, as is the case, for example, in the case of gas-blast switches which are insulated using SF6, the transmission linkage in the interior of the interrupter units must be designed. differently between the drive shaft and the moving switch contact piece in order to achieve identical connection and disconnection positions. However, the difference can be identified from the exterior only by suitable marking or by measurement, for example of the angle between the connected position and the separation of the contact pieces. There is therefore a risk of interrupter units being transposed during assembly and being assigned to incorrect. phases. Furthermore, a large number of different parts or adjustable parts are necessary, which leads to an increased supply-control and assembly cost.
A further power switch, which makes staggered switching possible, for high voltage is disclosed in EP-A-0541078. The switch has a single, continuous drive shaft which can be moved a reciprocating manner by means of the drive. A lever is assigned to each pole, which lever is arranged on this drive shaft in order to produce the staggering at a different rotation angle. In order to achieve identical connected and disconnected positions of the moving contacts and the same stroke in the interrupter units of all the poles, the levers and the insulating rods which connect the levers to the moving contact pieces must be designed to be of different length. Once again, the interrupter units of the switch differ from one another. In the case of a gas-insulated or liquid-insulated switch, in which the drive shaft is inserted into the poles in a sealed manner, this difference can, however, once again be detected from outside the interrupter units only by suitable marking or measurement. Once again, there is a risk of interrupter units being transposed during assembly, especially since, in order to implement four different switch variants, that is to say for 50 and 60 Hz and for staggered switching of all three poles or for time-delayed switching of one pole with respect to the two synchronously switching other poles, up to 10 variants of different interrupter units are required. In addition, the method of construction using a continuous drive shaft is unsuitable for relatively large switches, since such drive shafts do not have sufficient rotational stiffness and allow oscillations to start.